Design of Water and Wastewater Systems I
Design of Water and Wastewater Systems I CE 431
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Sedimentation CE 431 0 Why do we carewhere applied 0 After flocculation 0 Primary clarifier 0 Secondary clarifier o Grit removal 0 Reactor configurations circular square rectangular 0 Size 0 Plan view highly variable process specific function of flow rate 0 Depth application specific 0 Why 0 Freeboard 1 25 0 Operating mechanisms need to collect settled solids typically manufacture and application specific 0 4 defined modes of settling 0 Type 0 Type II 0 Type III 0 Type IV 0 Type Settling Lecture Notes Sedimentationdoc Lecture Notes Sedimentationdoc Lecture Notes Sedimentationdoc 0 Type II Settling o Flocs thus they settle faster as they increase in size 0 Primary clarifiers sedimentation of chemically coag dfloc d water 0 Theoretically requires batch settling tests to evaluate settling characteristics 0 Your book provides a brief description We ultimately design on the basis of overflow rate 0 Lecture Notes Sedimentationdoc 0 Primary Clarifier Design Approach Lecture Notes Sedimentationdoc 0 Primary Clarifier Design Issues Inlet velocity control Hydraulic StabilityShort Circuiting 0 Want to approach ideal basin conditions 0 How accomplished Temperature effects Wind effects Effluent control Typically use vnotch weirs for the perimeter effluent collection trough aka launder lnboard or outboard launders May need baffling to control solids washout Solids collection Typically utilize rakes on tank bottom to force solids to center where they are pumped out DO NOT use suction type collectors can plug Washington DOE do not allow gt 2 sludge layer to develop Need pumping system to withdraw solids from tank bottom Lecture Notes Sedimentationdoc 5 0 Primary Solids Handling Lecture Notes Sedimentationdoc Lecture Notes Sedimentationdoc Type III and Type IV Settling 0 000000 00 O 0 Both typically associated with flocculated particles Type III zone or hindered settling Particles are so close together that it hinders settling of nearby particles Hence particles all remain together and settle as a zone or mass Yields distinct solidliquid zone at the top of the settling mass Occurs within the intermediate depths of a secondary clarifier Also termed a blanket in activated sludge secondary clarification Type IV compression settling High concentration of particles thus can only settle through aggregationcompression Occurs at the bottom of secondary clarifier Secondary Clarifier Design Objectives 0 Separate biomass from water yielding the reclaimed water 0 Thicken settled solids to be returned RAS or wasted WAS to activated sludge basin 0 Temporarily store excess solids Efficiency is principally a function of the MLSS Design for existing activated sludge facilities apply the Solids Flux Analysis 0 Area required for thickening flimiting solids flux 0 Solids flux fMLSS 0 Perform column settling tests at variable MLSS concentrations Activated Sludge CE 431 0 Why do we employ activated sludge What does it really mean 0 Why not use physicalchemical treatment instead 0 Fundamental concepts 0 Wastewater flows into a tank or series of tanks that contain a high concentration of microorganisms 0 Certain environmental conditions are established that select for certain microorganisms We want to select forthe microorganisms that will ultimately perform the work we need completed 0 Remove carbon principally in soluble form nitrogen and phosphorus in the wastewater 0 Why do we care about these constituents Lecture Notes Activated Sludge Notesdoc 1 o What do these tanks look like How are they configured What are the principle structural elements How do we create these different environments Lecture Notes Activated Sludge Notesdoc o Microbiology Reactors contain bacteria protozoa fungi rotifers and nematodes Protozoa help control bacterial population and also consume colloids thereby enhancing effluent clarification 0 Their presence is a good indicator of a troublefree and stable process Importance of others not well defined Bacteria fundamentally perform most of the work 0 Many ways to classify 0 Classification phylogenetic 0 Classification carbon source Lecture Notes Activated Sludge Notesdoc 3 0 Classification Energy Source Bacterial nutrient requirements Table 1 Major elements their sources and functions in bacterial cells Element gagg try Carbon 50 Oxygen 20 Nitrogen 14 Hydrogen 8 Phosphorus 3 Sulfur 1 Potassium 1 Magnesium 05 Calcium 05 Iron 02 Source organic compounds or CO2 H2O organic compounds CO2 and O2 NH3 N03 organic compounds N2 H20 organic compounds H2 inorganic phosphates P04 804 H28 8 organic sulfur compounds Potassium salts Magnesium salts Calcium salts Iron salts Function Main constituent of cellular material Constituent of cell material and cell water 02 is electron acceptor in aerobic respiration Constituent of amino acids nucleic acids nucleotides and coenzymes Main constituent of organic compounds and cell water Constituent of nucleic acids nucleotides phospholipids LPS teichoic acids Constituent of cysteine methionine glutathione several coenzymes Main cellular inorganic cation and cofactor for certain enzymes Inorganic cellular cation cofactor for certain enzymatic reactions Inorganic cellular cation cofactor for certain enzymes and a component of endospores Component of cytochromes and certain nonheme iron proteins and a cofactor for some enzymatic reactions Lecture Notes Activated Sludge Notesdoc o Energetics and Gibbs Free Energy Lecture Notes Activated Sludge Notesdoc o Stoichiometry and Kinetics Lecture Notes Activated Sludge Notesdoc Water and Wastewater System Planning Under Planning we will cover the following critical elements which guide most of our designlevel decisions Regulations Population forecasting and related elements Water Supply planning elements Wastewater planning elements D My DocumenlSERC AcademCSCE 431leclure N0le5Leclure Notes 7 Planning doc Regulations Ultimately a primary factor in the planning and design of water and wastewater systems Federal regulations typically establish the base rules States then must typically adopt Federal as a minimum and can create more stringent laws Code of Federal Regulations gCFRL organized into Titles Chapters Subchapters Title 40 Protection of the Environment Chapter 1 Environmental Protection Agency ie 40CFR1 42 CF R6A Snbchapter XII Safe Drinking WuterAct SD WA 33CFR26 Clean Water Act CWA 42CFR85 Clean Air Act CAA 42CFR82 Resource Conservation and Recovery Act RCRA 42CFR103 Comprehensive Environmental Response Compensation and Liability Act CERCLA or Superfund 42CFR103 Superfund Amendments and Reauthorization Act SARA Safe Drinking Water Act Intended to protect public drinking water systems Application 0 1986 Amendments 0 set regulations for 83 contaminants by 1989 0 established ltration and disinfection requirements 0 ban use of lead pipes and solder 1996 Amendments 0 The requirement that EPA regulate an additional 25 contaminants every 3 years is eliminated o costbene t analysis for future drinking water standards 0 grants for communities to upgrade water treatment systems 0 consumer con dence reports CCRs by community water systems sets National Primary Drinking Water Standards NPDWS as Maximum Contaminant Levels MCLs for speci c pollutants 0 sets National Secondary Drinking Water Standards NSDWS to protect from aesthetic and odor problems in drinking water 0 Standards set by three step process 0 EPA identi es contaminants 0 EPA sets MCLG based only on risk 0 EPA sets MCL or Treatment Technique based on economic and technical feasibility Standards enforced by EPA and States Speci c Regulations 0 O O O D My D00urnenl5ERC Acadern05CE 431leclure N0le5Leclure Notes 7 Planning doc Clean Water Act 0 The Clean Water Act CWA is aimed at water pollution control 0 original enactment in 1948 0 provided funds for state water pollution control agencies 0 provided technical assistance to states 0 provisions for legal actions against polluters 0 completely revised by 1972 amendments netuned thereafter 0 The objective was to quotrestore and maintain the chemical physical and biological integrity of the Nation s watersquot 0 The implementation of these rules has had far reaching positive impacts on numerous water bodies throughout the nation effectively serving to create more quot shable and swimablequot conditions by establishing the basic structure for regulating pollutant discharges into water bodies 0 regulatory provisions for progressively more stringent requirements on industries and cities to meet the goal of zero discharge of pollutants o authorize federal nancial assistance for municipal wastewater treatment construction 0 CWA Section 305b National Water Quality Inventory Report 0 requires that each state periodically submit to the Environmental Protection Agency EPA a surface water quality assessment report that describes the water quality of all navigable waters within its borders 0 The quot305bquot list is relatively general and is used by the EPA to provide an update to Congress on the overall health of the nation s waters and the extent to which the Act has been successful 0 1998 National Report Highlights I 40 of assessed rivers lakes and estuaries not clean enough to support designated uses 32 of total waters assessed I leading pollutants include silt bacteria nutrients and metals I primary sources are runoff from agricultural lands and urban area 0 In Idaho I 67 of rivers impaired I pollutants include silt nutrients temperature bacteria habitat alterations Oz depleting substances I sources are undetermined o In Washington I Go to the following web site and research on your own httpwwwecywagovprogramswqwqhomehtml o CWA Section 303d Total Maximum Daily Loads TMDL 0 Under Section 303d of the Act every two years each state is required to develop a list of those surface waters for which existing pollution controls are not stringent enough to achieve that state s water quality standards These are known as Water Quality Limited WQL waters I Keeps State water quality regulatory agencies busy The quot303dquot list which is more detailed than the 305b list provides a means to prioritize water quality problems from which Total Maximum Daily Load TMDL plans can be developed to identify the causes of water quality problems and act to remedy the problem I The total amount of pollutant a waterbody can receive and still meet water quality standards it is a pollutant budget balanced at the point of the standard Calculated as the sum of point and nonpoint sources considering seasonal variability and a margin of safety 0 D My DocumenlSERC Academ05CE 431leclure N0le5Leclure Notes 7 Planmng doc 3 0 Water quality standards set by states tribes territories based on uses for each waterbody eg drinking water contact recreation aquatic life support and scienti c support for such uses 0 Also TMDLs specify pollutant reduction necessary to meet standards and allocates reductions among sources in the watershed Relationship between 305b and 303d 0 States are required to submit prioritized WQL lists under 303d every 2 years These lists are used to prioritize state restoration activities TlVlDLs o 305b data are used to assist in identi cation and priority ranking of 303d watersbut for 303d listings states may supplement the 305b data with other assessments or choose to only use the best data 0 The lists are generally consistent and conclude that silt nutrients bacteria and metals are among the top pollutants nationwide Section 304a 0 Under Section 304a the EPA periodically develops certain water quality criteria to help achieve the Act s goals and objectives These criteria which are based solely on water quality data and scienti c judgments and do not consider economic impacts or the technological capabilities to achieve such water quality are related to the information provided in the abovenoted water quality lists 0 Ultimately the 303d list must address those criteria developed through the 304a process Recent 304a application 0 In 1998 the EPA applied Section 304a and announced a plan to develop national nutrient water quality criteria On January 9 2001 and February 28 2002 the EPA formally published criteria in the Federal Register for nitrogen and phosphorus In addition to these causal parameters criteria were published for the response parameters turbidity and chlorophyll a The EPA divided the nation into 17 ecoregions with certain speci c criteria for each that were based on the individual region s geology physiography vegetation climate soils wildlife and hydrology I httpwwwepa ov Figures 1 and 2 show the proposed nutrient criteria by ecoregion The EPA s intent with these criteria is to achieve water quality conditions minimally impacted by human activities while providing desirable conditions for the growth and development of aquatic life and recreation States must adopt these new nutrient criteria by the end of 2004 State regulators can adopt less strict criteria but the approach and process must be defensible O O O OO O D My DocumenlSERC AcademlcSCE 431leclure N0le5Leclure Notes 7 Planmng doc 4 Igure Proposed EPA 304a Nitrogen Criteria Total Nitrogen Concentration mgL I II III N V VI VII VIII IX X XI XII XIII XIV Ecoregion I RiversStreams LakesReservoirs Figure 2 Proposed EPA 304a Phosphorus Criteria Total Phosphorus Concentration I II III N V VI VII VIII IX X XI XII XIII XIV Ecoregion I Rive rsStreams H La kesReservoirs o Cokgor et al 2000 report that four municipal biological nutrient removal BNR facilities in the Chesapeake Bay Watershed USA achieve ef uent ammonia concentrations ranging from 08 mgL to 36 mgL and total phosphorus effluent concentrations ranging from 021 mgL to 14 mgL A fth facility that incorporated chemical phosphorus treatment was capable of producing effluent concentrations of 006 mgL and 01 mgL respectively 0 Obenaus et al 2000 report on the performance of four large municipal BNR facilities in Germany which achieve over 75 removal of total nitrogen to less than 12 mgL N and over 85 removal of total phosphorus to less than 10 mgL P 0 Six municipal WWTPs in the northeast United States report average ef uent phosphorus levels of 006 mgL to 092 mgL Freedman et al 2000 Each of these plants which have capacities ranging from 014 million gallons per day mgd to 370 mgd utilizes BNR treatment in addition to chemical treatment for phosphorus removal D My DocumentSERC AcademicSCE ASIlecture NoteSLecture Notes 7 Pianning doc 0 National Pollutant Discharge Elimination System NPDES permits 0 Issued for the discharge of water into Waters of the StateNation 0 Examples I Wastewater treatment facilities discharging reclaimed water into lakes and rivers I Water treatment plant backwash water discharges I Stormwater discharges 0 Typical permit see handout D My D00urnenl5ERC Acadern05CE 431leclure N0le5Leclure Notes 7 Planning doc RCRA Resource Conservation and Recoverv Act 1976 addresses how hazardous wastes are handled at existing and new facilities does not deal with abandoned or closed facilities Major Elements 0 federal classi cation system 0 cradle to grave manifest system 0 federal standards for safeguards to be followed 0 enforcement of federal standards for facilities through a permit program 0 authorization of state programs to operate in lieu of the federal program RCRA Subtitle C Hazardous Waste Management RCRA Subtitle D Solid Waste Management 0 municipal solid waste MSW and nonhazardous industrial waste 0 establishes standards for solid waste land lls to ensure safe management of MSW CERCLA Comprehensive Environmental Response Compensation and Recovery Act in general CERCLA gives the federal government authority to remove hazardous substances from dangerous inactive disposal sites and assist with cleanup establishes prohibitions and requirements concerning closed and abandoned waste sites it provides for liability of responsible persons establishes a trust fund to pay for cleanup when responsible persons can not be identi ed short term response where action must be take to address releases or threatened releases that require prompt response long term remedial response actions to permanently and signi cantly mitigate serious but not immediately life threatening situations National Contingency Plan NCP federal action plan for responding to oil and hazardous substance releases National Priorities List NFL to use CERCLA funds for remedial action site must be on NFL Hazardous Ranking System HRS used to place uncontrolled waste sites on the NFL D My DocumenlSERC AcademlcSCE 431leclure N0le5Leclure Notes 7 Planmng doc 7 2 Service LifeDesign PeriodPopulation Forecasting We size and design infrastructure to accommodate growth not based on current needs Service Life versus Design Period 0 Service Life expected useable life of infrastructure 0 Mechanical systems 25 years 0 Piping eg sanitary sewer systems water distribution systems 50 to 100 years 0 Structures water tanks wastewater treatment structures 50 to 100 years 0 0 Design Period population planning period for designingsizing infrastructure 0 Typically work on 25 year minimum planning periods 0 Also need to consider buildout populations 0 What drives the 25 year timeframe 0 Sometimes the two overlap sometimes not 0 eg collection system wastewater pumping station mechanical vs structural Population Data 0 Historical population data 0 US Census decennial counts eg 10 year intervals 0 State local other annual estimates 0 Contrast with similar cities 0 School enrollments 0 Utility connections 0 Land use data 0 Latter three require population factor estimate 0 eg 31 for typical utilities 0 socioeconomically in uenced o residentialcommercialindustrially in uenced Population Forecasting o More of an art than science 0 Relies on experience and understanding of local socioeconomic conditions 0 Factor in potential buildout boundaries and buildable lands inventory 0 Ultimately may need to coordinate population with the State 0 eg Oregon D My DocumenlSERC AcademlcSCE 431leclure N0le5Leclure Notes 7 Planmng doc Population Forecasting Models 0 Constant Percentage Method 0 Linear on semilog paper 0 Linear Model 0 Constant rate of growth 0 Linear on arithmetic paper 0 Curvilinear method 0 Which model is most appropriate D My DocumenlSERC AcademlcSCE 431leclure N0le5Leclure Notes 7 Planmng doc 3 Water System Planning Water Dem ands Design ows are based on the type of usage associated with the facility being constructed Need to consider public municipal industrial and commercial usage Municipal Planning need to identify top users Consider average minimum maximum and peak ow conditions 0 O 0 Also consider unaccounted for water 0 Lea s o Pipeline breaks 0 Unauthorized service connections 0 Improperly operating meters 0 Recommended to be less than 15 o In estimating best to account for as much usage as possible I Separate out unmetered but known usage Forecasting need to incorporate more ef cient use of water in the future What are some typical average water usage numbers and maxmin factors How do we develop this data for our speci c situation eg City commercial building apartment complex D My DocumenlSERC AcademlcSCE 431leclure N0le5Leclure Notes 7 Planmng doc 0 General Design Factors 0 Sizing raw water and nished water supplies including transmission and treatment I Maximum Day Demand MDD I Often provide some level of reliabilityredundancy plus some excess capacity in individual units 0 Storage sizing I One general approach 0 O I Ground level versus Elevated tanks critical to understand hydraulics and necessary appurtenances to provide required ow I Each Statejurisdiction may have their own storage sizing criteria 0 Washington 0 Distribution system I PHF re ow D My DocumenlSERC AcademlcSCE 431leclure N0le5Leclure Notes 7 Planmng doc 11 Water Quality 0 Common Contaminants raw water 0 Surface Water 0 Ground Water 0 Common Contaminants nished water D My DocumentSERC AcademCSCE 431lecture N0te5Lecture Notes 7 P anmng doc 0 Bulk Parameters 0 Physical o Turbidity 0 Color 0 TasteOdor 0 Temperature 0 0 Chemical D My DocumenlSERC AcademlcSCE 431lecture N0le5Leclure Notes 7 Planmng doc 0 General review of chemical calculations D My DocumenlSERC AcademlcSCE 431leclure N0le5Leclure Notes 7 Planmng doc 4 Wastewater System Planning Wastewater Flows 0 Commercial Industrial rely on such information as xture units usespeci c data as provided by your client or obtained from similar facilities and the various general references Municipal typically base our design ow analyses on actual treatment plant data Sources of municipal wastewater 0 Domestic o In ltration o In ow Similar diurnal pattern to water usage Pertinent ow factors see Oregon DEQ handout 0 Average Daily Flow 0 Peak Day 0 Peak Hour 0 Maximum and Minimum Month 0 Minimum Day 0 What is the relevance of each D My DocumenlSERC AcademCSCE 431leclure N0le5Leclure Notes 7 Planmng doc 15 Wastewater Constituents see also the example NPDES permit 0 Physical D My DocumentSERC AcademCSCE 431lecture N0te5Lecture Notes 7 P anmng doc o Inorganics o Metals D My DocumentSERC AcademCSCE 431lecture N0te5Lecture Notes 7 P anmng doc o Organics oxygen demand D My DocumentSERC AcademCSCE 431lecture N0te5Lecture Notes 7 P anmng doc o Microorganisms D My DocumentSERC AcademCSCE 431lecture N0te5Lecture Notes 7 P anmng doc Filtration CE 431 o What decisions are made in the design of a ltration process We ll work through an example 0 Q l mgd 0 Use rapid ltration 0 Single media lter 9 Sand 0 Filter medium characteristics 9 Grain size principle characteristic of interest I T00 small driving head wasted to overcome friction I T00 large inef cient ltration I Size distribution determined through sieve analysis 0 Effective size d10 sieve size mm to pass 10 by wt 0fthe sand 0 Uniformity coef cient UC d50d10 o d50dia by which 60 0f the media by wt is smaller 0 typically 1317 I As the engineer you specify the grain size distribution for the type of ltration you are using 9 see attached typical design data Tables 118 and 119 0 For our example assume a conventional lter 39 C110 065 I UC 14 I To determine clean water headloss use the Rose equation D My DocumentSERC AcademlcSKZE 431lecture N0te5Lecture Notes 7 Flltrallon doc I Example continued D My DocumentSERC AcadermcSKZE 431lecture N0te5Lecture Notes 7 FHtrann doc Nuw we have an esnmaze ufmlmmum head luss Nhatthpms m a ner uvernme7 1 l1 um Lam and mum mng mm In w Dp nmm Perannual mun In my mu 1 Huw an we desxgq a 51mm sysLem m upnmze sue run tame and zvmd prer mature cluggny Huw an we desxgq the lter such Lhatthe meduwxll settle mm the same general gadauun fulluwmg backvasm I Filter Backwash calculation Settling Velnklw v mm 10 ID x 10 Pamela manual vi an FIGURE 95 me 1 Stirling uISphlre In quotmm a are mm y r R Camp pl Bum quotMm mmmemquot u in Handbook 0 Appllul Hydraulic 2nd rd am by c vl Dam mpyngm 1951 by Mchwlml m Repnnmd by pcrmmuu D Mv DucumemsERC AcademmsCE 631Lecuve NulesLecluve Nulesr Fmvalmn an I Continued D My DocumentSERC AcadermcSKZE 431lecture N0te5Lecture Notes 7 FHtrann doc I How are lters cleaned 0 Estimating maximum head loss I Modify the clean water headloss equation to account of decreased porosity o Difficult to do accurately I Pilot tests you will work through a homework problem I Experience I Other facilities drawing from the same water source 0 Filter media selection criteria 9 engineers often specify filter media gradation 39 C110 I UC I 90 size by weight I Specific gravity I Hardness I Depth of various materials used in the filter 0 Some other filtration design criteria issues I Quality of water being treated 0 Particle sizes 0 Soluble organics I Ef uent requirements I LOTS of hydraulics pumping piping effluent troughs I Add chemical for filtration aid I How many filters I How to manage solids I Instrumentation and control D My DocumentSERC AcademCSCE 431lecture N0te5Lecture Notes 7 Filtration doc CHAPTER 9 RESERVOIR DESIGN AND STORAGE VOLUME In accordance with engineering standards of care reservoirs are to be designed to provide stability and durability as well as protect the quality of the stored water For any particular project there may be more than one acceptable reservoir design concept The reservoir design criteria are not intended to establish any particular design approach but rather to ensure water system adequacy reliability and compatibility with existing and future facilities 90 Storage Volume Components For a given reservoir design each of the ve 5 storage component listed below as discussed in Section 673 must be considered WAC 2462902353 Operational storage OS Equalizing storage ES Standby storage SB Fire suppression storage FSS and Dead storage DS if any 959 Figure 91 illustrates and Table 91 describes a typical crosssection of the reservoir storage components Section 905 provides the basis for determining when the smaller of the SB or FSS components may be deleted from the total storage volume Section 913 provides guidance for reduction or elimination of the storage volumes as defined below Only effective storage as defined in Section 901 may be used in determining the actual available or design storage volume 901 Effective Storage Total tank volume as measured between the over ow and the tank outlet elevations may not necessarily equal the effective volume available to the water system Effective volume is equal to the total volume less any dead storage built into the reservoir For example a standpipe has a component of its capacity which is intentionally designed as dead storage meaning that below a certain water surface elevation within the tank the pressure delivered to some customers falls below minimum pressure requirements for the system Conversely if a water system s source well or booster pump is not capable of delivering a design rate of ow above a certain water surface elevation within the tank then this upper volume of the tank is considered unavailable to the system and is not a part of the effective storage Water System Design Manual August 2001 91 The amount of effective storage may also be dependent upon the location of the storage relative to the place of its use whether or not it is in a different pressure zone and what distance the water needs to be conveyed 902 Operational Storage OS Consistent with the definition presented in WAC 246290010 operational storage is the volume of the reservoir devoted to supplying the water system while under normal operating conditions the sources of supply are in off status This volume will vary according to two main factors 1 the sensitivity of the water level sensors controlling the source pumps and 2 the configuration of the tank designed to provide the volume required to prevent excessive cycling starting and stopping of the pump motors The definition specifies that OS is an additive quantity to the other components of storage This provides an additional factor of safety to the ES SB and FSS components if the reservoir is full when that component of storage would be needed Water level sensors may vary from mercurytype oat switches to ultrasonic sensors to pressure switches Each type has a different sensitivity to water level changes from fractions of inches to more than a foot The tank designer will have to account for the type of level sensor specified when determining the vertical dimension needed for proper operation of the device Manufacturer s specifications generally govern the determination of this dimension Once the pump control device is selected the tank designer will be able to factor in the vertical dimension when determining the other aspects of tank configuration such as the width and height as well as the shape The volume of OS should be sufficient to avoid pump cycling in excess of the pump motor manufacturer39s recommendation Historically a rule of thumb was to limit the motor to no more than siX starts per hour However many manufacturers will warrant more frequent cycling for their pump motors depending upon the size of the pump The OS volume determined in this situation is comparable to the withdrawal volume required when using hydropneumatic tanks for pump motor protection Ten States Standards recommends that the gross volume of the hydropneumatic tank in gallons be at least ten times the capacity of the largest pump rated in gallons per minute Withdrawal volume of a hydropneumatic tank is usually on the order of 25 of the gross volume Using this relationship it would be recommended that the OS volume be about 25 times the capacity of the largest pump Calculating the OS volume will verify that typically for gravity storage tanks it is substantially less than the remaining volume of the tank The volume associated with the elevation difference required for the pump level sensors is usually larger than that required for pump motor protection so that volume generally becomes the limiting factor when determining the OS volume required Operational storage does not apply to systems operating under a continuous pumping mode see Section 903l Under this situation pump motor protection is assured by the operational mode and the other components of effective storage ES SB and FSS are all that need to be considered Water System Design Manual August 2001 92 903 Equalizing Storage ES When the source pumping capacity cannot meet the periodic daily or longer peak demands placed on the water system Equalizing Storage ES must be provided WAC 2462902352 as a part of the total storage for the system and must be available at 30 psi to all service connections The volume of ES depends upon several factors including peak diurnal variations in system demand source production capacity and the mode of operation either continuous pumping for a select period of time or by callondemand through use of reservoir level control switches Each water system should be evaluated based on its mode of operation and hydraulic capabilities 1 Continuous Pumping The method for determining ES requirements depends upon the mode of source pump operation If pumping is to be continuous for a period of time sufficient to provide the total maximum day demand it is necessary to prepare a mass analysis by either graphical or tabular methods or a computer simulation Varying system head curves and demand scenarios should be evaluated to determine the maximum ES volume required by the system 2 Call On Demand Equation 91 shown below should be used for estimating minimum ES requirements unless actual water use records indicate a more applicable volume Water systems with multiple sources may need to provide ES in excess of Equation 91 depending upon the mode of operation This may involve storing multiple days of volume to meet maximum system demands Equation 91 ES PHD Qs 150 min but in no case less than zero Where ES Equalizing storage component in gallons PHD Peak hourly demand in gpm as de ned in Chapter 5 ofthis manual Sum of all installed and active source of supply capacities except emergency sources of supply in gpm See Section 911 for the definition of source Qs 904 Standby Storage SB Water System Design Manual August 2001 93 The purpose of SB is to provide a measure of reliability should sources fail or when unusual conditions impose higher demands than anticipated The SB volume recommended for systems served by one source may be different than for systems served by multiple sources as described in the following sections 1 Water Systems With A Single Source The recommended SB volume for systems served by a single source of supply is two 2 times the system s average day demand ADD for the design year to be available to all service connections at 20 psi ADD is de ned in Chapter 5 of this manual Equation 92 SBTSS 2 days ADD N Where SBTSS Total standby storage component for a single source system in gallons ADD Average day demand for the design year in gpdERU and N Number ofERUs 2 Water Systems With Multiple Sources The recommended SB volume for systems served by multiple sources should be based upon the following equation Equation 93 SBTMS 2 daysADDN tm QS QL Where SBTMS Total standby storage component for a multiple source system in gallons ADD Average day demand for the system in gpdERU N Number ofERUs Qs Sum of all installed and continuously available source of supply capacities except emergency sources in gpm See Section 911 for the definition of a continuously available source QL The largest capacity source available to the system in gpm tm Time that remaining sources are pumped on the day when the largest source is not available in minutes Unless restricted otherwise this is generally assumed to be 1440 minutes Note Although SB volumes are intended to satis the requirements imposed by system customers for unusual situations and are addressed in WAC 246290 420 it is recommended that the SB volume be not less than 200 quotallonsERU Water System Design Manual August 2001 94 3 Standby Storage SB for Recreational and Non Critical Commercial Uses There is no recommendation for SB for systems made up entirely of the following noncommunity uses 1 RV parks 2 camp grounds 3 fair grounds 4 outdoor concert grounds 5 restaurants and 6 noncritical commercial uses It is generally assumed that these systems could reasonably be shut down in the event of a loss of water supply without impacting public health and welfare There is also no recommendation for SB for recreationalresidential water systems those systems used predominantly for recreational purposes that do not permit through covenant or other means nor do they currently have any permanently fixedinplace residential structures Schools hospitals and recreational residential water systems serving permanent fixed in place residential structures are examples of non community systems for which the SB recommendation applies 4 Standby Storage SB for Non Community Uses SB for nontransitory noncommunity water systems with a single source should be the same as defined in Section 9041 SB for nontransitory noncommunity water systems with multiple sources should be the same as defined in Section 9042 Noncommunity water demands must be determined as defined in WAC 2462902212 Chapter 5 of this manual presents some recommended criteria that apply to noncommunity water uses 5 Reduction in Standby Storage The purveyor and system designer have a number of options available to decrease the volume of SB in the system As indicated in item 2 above the volume may be reduced with development of additional sources of supply To be considered equivalent to gravity storage the sources would also need to be equipped with auxiliary power that starts automatically when the primary power feed is disrupted The purveyor may also reduce the volume if community expectations are amenable to a lesser SB capacity such as their agreeing that the volume for one average day of service would be sufficient for standby purposes instead of two days A utility may also make better use of dead storage by providing booster pumps at the point where the pressure reaches the minimum established by the community in situations when the SB is used Water System Design Manual August 2001 95 905 Fire Suppression Storage FSS Public water systems are required to construct and maintain facilities including storage reservoirs capable of delivering re ows in accordance with the determination of fire flow requirement made by the local re protection authority or County Fire Marshal while maintaining 20 psi pressure throughout the distribution system WAC 2462902215 The magnitude of FSS is the product of the maximum ow rate and duration established by the local re protection authority or County Fire Marshal For water systems located in areas governed under the Public Water System Coordination Act of 1977 PWSCA Chapter 70116 RCW minimum ow rates and durations that must apply for residential commercial and industrial developments are speci ed in the Water System Coordination Act regulations WAC 246293 640 Greater FSS requirements may be speci ed by the local re protection authority County Fire Marshal and or locally adopted Coordinated Water System Plan Minimum FSS Volume The minimum FSS volume for systems served by a single source of supply or multiple sources of supply is the product of the required ow rate expressed in gpm multiplied by the ow duration expressed in minutes Equation 9 4 FSS FFtm Where FF Required fire flow rate expressed in gpm as specified by fire protection authority or the Coordination Act whichever is greater and tm 7 Duration of FF rate expressed in minutes as specified by fire protection authority or the Coordination Act whichever is greater Special Note SB and F SS Consolidation Nesting The SB component or the FSS component whichever volume is smaller can be excluded from a water system 39s total storage requirement provided that such practice is not prohibited by 1 a locally developed and adopted Coordinated Water System Plan 2 local ordinance or 3 the local fire protection authority or County Fire Marshal See WAC 246 290 2354 906 Dead Storage DS Dead storage effective only to provide adequate pressure is the volume of stored water not available to all consumers at the minimum design pressure in accordance with WAC 246290 2305 and 6 DS volume is excluded from the volumes provided to meet OS ES andor FSS Water System Design Manual August 2001 96 requirements Local community standards apply as to whether or not some DS volume may be used to provide SB volume to meet minimal community expectations during unusual operating conditions 907 Storage Used for Treatment Purposes Sometimes storage volume is needed to provide adequate contact time for routine disinfection practices or to meet surface water treatment requirements See SWTR Guidance Manual When storage volume is provided to meet a water treatment requirement the designer will be required to determine the volume necessary They will also need to describe how the reservoir design and con guration will provide adequate treatment and public health protection under all reasonably anticipated operating conditions The FSS andor SB volume should not be considered as part of this volume and the designer should clearly articulate to the system owner that the risk to public health will increase if or when the storage volume is decreased and eventually depleted It is also important to understand that a Treatment Technique Violation can occur whenever insufficient storage is available to provide the disinfectant contact time required The owner and or community may desire to increase the storage volumes provided to reduce that risk DOH recommends that storage volume required to meet surface water treatment requirements be separate from the distribution storage provided 91 Reservoir Sizing Considerations All storage volumes may be reduced if source water is reliably available to meet all demands at the required ow rate and duration Following are some elements to evaluate when considering reductions for the designed storage volumes 911 Definition of Source as Used in Sizing New Reservoirs Any source classified as either permanent or seasonal may be considered a source for the purpose of designing new reservoir facilities provided that the source is continuously available to the system and at a minimum meets all primary drinking water standards WAC 246290010 2223 and 4202 amp 5 To be continuously available to the system means that l the source is equipped with functional pumping equipment and treatment equipment if required 2 the equipment is exercised regularly to assure its integrity 3 water is available from the source year round and 4 the source is activated automatically based on preset parameters reservoir level system pressure etc For the purpose of designing new reservoir facilities the following are considered sources 1 Each pump in a booster pump station pumps installed in parallel not series pumping into the zone served by that particular reservoir 2 Each independent parallel treatment train in a water treatment facility Water System Design Manual August 2001 97 3 Each well or well eld comprised of wells constructed per Chapter 173160 WAC Minimum J J for Construction and 39 of Wells and capable of pumping concurrently as justi ed by actual pump test records 4 Each pump installed in a large capacity large diameter well provided that each pump can be taken out of service without the need to interrupt operation of any other pump 5 An emergency intertie provided that l the intertie is equipped with an automatic valve 2 the intertie agreement speci cally includes provision of SB and or FSS and 3 the intertie supplying and receiving distribution systems have suf cient hydraulic capacity to deliver the allocated ow at no less than the minimum pressure required by WAC 246290230 If the intertie requires boosterpumping facilities then each pump installed in parallel constitutes a source 0 A pressure reducing valve between pressure zones within the same system provided that l adequate volume is available in the upper zone s storage facilities and 2 the distribution system from the upper zone through the PRV to the end use in the lower zone has suf cient hydraulic capacity to deliver the allocated ows whether they are to meet or augment peak hour ows or re ows at no less than the minimum pressure required by WAC 246290230 The actual installed capacity of the facilities and equipment is to be used when determining service capacity based on storage requirements for existing systems 912 Storage for Consecutive Systems A consecutive water system those systems which purchase all of their water supply from another regulated water system may utilize the storage available from the supplying system to satisfy the requirements of Chapter 9 provided that l The wholesale water agreement between the supplying system and the consecutive system de nes the quantity of ES SB and FSS operated by the supplying system that is speci cally reserved for the consecutive system and N It can be demonstrated that both the supplying and consecutive system can satisfy the hydraulic design criteria described in Sections 823 and 93 913 Alternate Design Concept The ES and SB components summarized in Section 90 may be reduced or in some instances eliminated provided that the water system design includes multiple sources of supply and in some cases onsite standby power ES may be eliminated only if the combined capacity of the sources of supply meets or exceeds the PHD for the system andor the pressure zone with 30 psi pressure provided at each existing and proposed service connection The FSS component of storage design may be reduced or in some cases eliminated provided the water system design includes onsite standby power and the system is served by multiple sources of supply that are Water System Design Manual August 2001 98 capable of providing the re ow rate in addition to the MDD rate for the system This should be veri ed with the local re protection authority Water systems substituting source capacity for storage volumes need to consider and provide appropriate justi cation for varying from the following criteria 1 Exclude the capacity of the largest producing source of supply from the calculations 2 Each source of supply used in the calculations be equipped with onsite backup power facilities promptly started by an automatic transfer switch upon loss of utility power 3 Incorporate provisions for pump protection during low demand periods into the system design 914 Design Life Storage facilities are normally designed to serve the needs of the community for a planned number of years or to accommodate full system buildout if they serve a particular subdivision or planned development or ful ll a condition of plat approval etc The design life for properly maintained concrete and steel storage tanks is typically assumed to be about fty years Any other type of storage tank that does not have the historical longevity of these tanks needs to be evaluated on a life cycle cost basis before being considered for use 92 Establishing Overflow Elevations Considerations for establishing over ow elevations for reservoirs designed to provide gravity water service include 1 Consistency With Other Facilities and Plans The over ow elevation should be consistent with other storage facilities in use or planned by the water system Over ow elevation of existing or proposed facilities of other nearby water systems should also be considered Equot Consistency With Pressure Requirements and Limits The tank over ow elevation should be consistent with pressure requirements and pressure limitations within the existing and future water service area The designer should consult topographic maps in addition to information received from the system hydraulic analysis described in Section 82 Equot Consistency With Source Capacity Tank elevation and tank geometry should be coordinated with source equipment dischargehead characteristics to assure that source capacity requirements established by DOH are met Pump curves should be developed and detailed hydraulic analyses Water System Design Manual August 2001 99 prepared of existing and future distribution system conditions pipe network and water demand 4 Maintaining Levels To assure levels are maintained in reservoirs throughout the system use altitude valves where appropriate 93 System Pressure Considerations The hydraulic design criteria for new and existing water systems is described in this section Figure 91 provides a graphic View of the reservoir hydraulic design criteria described below Chapter 5 of this manual de nes peak demand periods including the maximum day demand MDD and peak hourly demand PHD 931 Fire Suppression Storage FSS Component For systems supplied through gravity storage the bottom of the FSS component must be located at an elevation which produces no less than 20 psi at all points throughout the distribution system under the ow conditions MDD rate plus re ow described in WAC 2462902306 Where some of the re ows are supplied by pumping it is recommended that the analysis be completed assuming that the largest source is out of service This assumption and analysis is required where section 660 of the Water System Coordination Act Chapter 246293 WAC applies Any one or combination of design parameters including the tank elevation tank geometry tank location andor the distribution piping network may be modi ed to meet the 20 psi residual pressure standard The design engineer is responsible for providing evidence of a hydraulic analysis as per Section 82 of this manual 932 Standby Storage SB Component The lower elevation of the SB component should be that which produces no less than 20 psi at all existing and proposed service connections throughout the distribution system under PHD conditions assuming that the largest source is not in service Any one or combination of design parameters including the tank elevation tank geometry tank location andor the piping network may be modi ed to meet the 20 psi residual pressure The design engineer is responsible for providing evidence of a hydraulic analysis as per Section 82 of this manual Water System Design Manual August 2001 910 933 Consolidation Nesting of Standby SB and Fire Suppression Storage FSS If consolidation of SB and FSS is proposed as allowed per WAC 2462902354 the evaluation of storage volume elevation must be completed per Section 931 above The evaluation at higher elevations or pressures would only be necessary if the local community establishes a higher level of service for conditions under which standby storage is used 94 Site Feasibility Considerations Site feasibility considerations should include 1 Sufficient area to construct and maintain the facility as well as allow room to site additional storage to meet projected growth 2 Distance to the existing distribution and transmission system 3 Need for new distribution and transmission pipelines to meet pressure standards 4 Existing ground surface elevation and site drainage 5 Site access anticipating potential seasonal limitations 6 Geotechnical engineering field investigations including a foundation design requirements b soil typesoil bearing strength and c ground water table elevation 7 Availability of power 95 Special Design Considerations Based on Type of Reservoir Special design considerations for reservoirs and storage tanks should include 951 Backup Power Recommendations For NonElevated Reservoirs DOH recommends that systems relying on nonelevated reservoirs ie reservoirs that can only supply a distribution system in whole or in part through a booster pump station be equipped with onsite backup power facilities or at least with the ability to readily connect to a portable generator Booster pump design guidelines are described in Chapter 10 of this manual It is also recommended that the backup power facilities be designed to start through an automatic transfer switch upon interruption of the utility power supply Manual transfer may be sufficient providing it can be done within a reasonable time period in accordance with established Water System Design Manual August 2001 911 operating procedures The primary intent for recommending backup power is to assure that the system is pressurized at all times to minimize crossconnection contamination concerns 952 Ground Level and Underground Reservoirs The following recommendations apply to ground level partially buried and underground reservoirs 1 Ground level partially buried and underground reservoirs should be placed outside the lOOyear ood plain N The area surrounding a ground level or below grade reservoir should be graded in such a manner that will prevent surface water from standing within 50 feet of the structure at a minimum E When the reservoir bottom is below normal ground surface it should be placed above the groundwater table if possible If this is not possible special design considerations should include providing perimeter foundation drains to daylight and exterior tank sealants These are necessary to keep ground water from entering the tank and to protect the reservoir from potential otation forces when the tank is empty 4 Partially buried or underground reservoirs should be located at least 50 feet from sanitary sewers drains standing water and similar sources of possible contamination Pipe typically used for water mains should also be used for gravity sewers if they are located within 50 feet of the reservoir These pipelines should be pressure tested in place to 50 psi without leakage V39 The top of the reservoir should not be less than two feet above normal ground surface unless special design considerations have been made to address maintenance issues and protection from surface contamination 953 Tank Materials in Contact with Potable Water All additives coatings and compounds proposed for use in substantial contact with potable water such as those listed below must have ANSINSF certi cation per WAC 246290220 for contact with potable water These materials also need to be carefully applied in accordance to the manufacturer s recommendations for that particular material To avoid unnecessary public health concerns and consumer complaints regarding aesthetic qualities the design engineer should address the following concerns 1 For concrete tanks use appropriate form oils concrete surface sealants and curing compounds or plasticizers N For steel tanks consider the materials used to prepare the surface of the tank as well as the painting or coating systems used to protect against corrosion Cathodic protection should be provided as necessary especially for underground or partially buried tank installations Water System Design Manual August 2001 912 3 Reservoirs employing membrane liners plastic tanks or other alternate designs should be ANSINSF certi ed 4 Temperature time and ventilation conditions as well as the thickness of the applied layers speci ed for proper curing of coatings are critical elements to assure protection against the leaching of undesirable levels of substances into the water In circumstances where there is any concern over the curing of the coatings and materials applied or over the leachability of the reservoir liner DOH may require additional water quality monitoring on water drawn from the reservoir prior to the reservoir being placed into service Refer to Appendix H for additional guidance regarding leach able materials testing 96 Reservoir Appurtenant Design All reservoir appurtenances should be designed to be water tight and must WAC 246290 235l have means to prevent entry by birds animals insects excessive dust and other potential sources of external contamination including crossconnections All reservoir appurtenances should be designed to protect against freezing and ice damage which will interfere with proper functioning such as tank level controls riser pipes over ows and atmospheric vents 961 General The following elements should be considered as part of the overall reservoir appurtenances design 1 Installed reservoir isolation valves which permit isolating the tank from the water system A provision for tank isolation is required per WAC 246290235l 2 Installed air releasevacuum release valve on the distribution system side of the isolation valve 3 Installed sample tap on the tank side of the isolation valve A provision for sample collection capability is required in the reservoir design per WAC 246290235l 4 Installed high level and low level alarm system with direct annunciation or notification to operations personnel 5 Installed local level indication either by a pressure gauge measured in quotfeetquot or by an exterior site gauge 6 Designed and installed drain facilities Section 962 7 Designed and installed over ow pipe Section 963 8 Tank atmospheric vents with a noncorroding insect screen as described in Section Water System Design Manual August 2001 913 9 Designed with locks on all hatches access entries sites fences and access ladder extensions to prevent unauthorized entry and vandalism 10 Designed with water tight insect proof access hatches ventsWAC 246290235l 11 Access ways and ladders necessary to provide safe maintenance access 12 Lightning arresters and electrical grounding as applicable 13 Removable siltstop on the outlet pipe 14 Leakage testing and disinfection per accepted standards such as AWWA 15 Slope of reservoir roof at a minimum of 2 14quot per foot 16 Piping material below the reservoir and extending at least 10 feet from the perimeter of the structure constructed of sturdier materials as indicated in Section 966 17 Separate inlet and outlet pipes to and from the reservoir to allow for effective turnover of the stored water These pipes should be on opposite sides of the reservoir and preferably at different elevations to prevent or minimize short circuiting 962 Reservoir Drains Reservoirs must be designed with drain facilities that drain to daylight or have an approved alternative that is adequate to protect against crossconnection contamination WAC 246290 235l The facilities should be capable of draining the full contents of the tank without entry to the distribution system or causing erosion at the drainage outlet Any connection to storm sewers or sanitary sewers is not recommended unless special circumstances or design features assure negligible risk of crossconnection contamination The preferred method for cross connection protection would be the provision of a minimum two 2 pipe diameter air gap In locations where the topography is such that a drain to daylight is not feasible the reservoir should be designed with a sump to allow for emptying the reservoir through use of a sump pump If an outlet pipe is also used as a reservoir drain it should include a removable silt stop in the reservoir Drain lines may discharge directly to a dedicated dry wells provided precautions are designed and constructed to insure protection against back ow into the reservoir or distribution mains 963 Reservoir Overflows Reservoirs must be designed with an over ow pipe with atmospheric discharge or other suitable means to prevent a crossconnection WAC 246290235l The over ow pipe should be designed to convey ow in excess of the design maximum supply rate to the reservoir The over ow piping should also be designed such that over ow discharge will not cause erosion at the outlet Any direct connection to storm drains or sanitary sewers is not recommended unless special circumstances or design features assure negligible risk of crossconnection Water System Design Manual August 2001 914 contamination A recommended method would be the provision of a minimum two 2 pipe diameter air gap at the outlet Over ow lines should have a noncorrodible mesh screen or mechanical device secured over its discharge end or preferably within the pipe to reduce susceptibility to damage by vandalism If mesh is used No 24 noncorrodible mesh or 1 1s 964 Reservoir Atmospheric Vents Reservoirs must have a screened roof vent per WAC 2462902350 Over ows are not considered to be vents To be effective vents should be able to allow air into the reservoir at a rate greater than or equal to the rate that the water is withdrawn from the reservoir to prevent implosion or structural damage to the reservoir The design should consider how to keep the vents from getting plugged or restricted and how to protect from frostingfreezing up or vandalism Upward facing vents must not be used in any application Screens must be provided on the vents to prevent entry by birds or animals For elevated tanks and standpipes No 4 mesh non corrodible screen may be used Ground level or underground reservoirs should terminate in an inverted U construction with the opening 24 to 36 inches above the roof or ground and covered with No 24 mesh noncorrodible screen Screens on groundlevel reservoir vents should be located within the pipe at a location minimally susceptible to vandalism 965 Roof Drainage The roof of the reservoir should be well drained The slope of the reservoir roof should be a minimum of 2 14 vertical per foot horizontal To avoid possible contamination downspout pipes must not enter or pass through the reservoir WAC 246290490 966 Piping Material Piping material used for pipelines constructed directly below the reservoir and extending to at least 10 feet from the perimeter should be sturdier material such as ductile iron pipe or AWWA C205 steel pipe with a corrosion resistant coating inside and out Once the reservoir is in place it is relatively difficult and expensive to repair or replace such pipe should it be broken or damaged due to differential settling or movement of the reservoir or due to corrosion 97 Operational Constraints and Considerations All new reservoir designs are expected to meet all applicable OSHA and WISHA requirements In addition reservoir design and construction should consider the following issues 1 Disposal of chlorinated water after construction and disinfection Water System Design Manual August 2001 915 N Disposal of tank drain line out ow and tank over ow stream E Impacts to system operation if the new reservoir were to be taken offline in the future for maintenance and or cleaning 971 Valving Reservoir design must include a provision for tank isolation per WAC 2462902350 in order to be able to perform maintenance This may be accomplished by providing an isolation valves which permit isolating the tank from the water system An air releasevacuum relief valve should be installed on the distribution side of the isolation valve A sample tap should be installed on the tank side of the isolation valve to allow for the required sample collection capability 972 Tank Level Control All new reservoirs should be equipped with a level control system designed to maintain reservoir water levels within a preset operating range operating storage As a minimum the normal high and normal low water surface elevations that define this operating range should be specified in the design A high level and lowlevel alarm system with direct annunciation of notification to operation personnel should be installed There should also be a local level indication either by a pressure gauge or by an exterior site gauge measured by feet Cablesupported oat switches are inappropriate under conditions in which there is a potential for ice formation in the reservoir Under these conditions alternate means of tank level control and monitoring should be evaluated 98 Reservoir Structural Design Seismic risk must be taken into account when designing reservoirs WAC 246290200 Refer to Chapter 13 Section 1352 for additional guidance on seismic design ofreservoirs Water System Design Manual August 2001 916 Table 91 Reservoir Storage Component CrossSection Diagram High Level Alarm Over ow above pump 0Q elevation Pump Off Operational Storage OS Component Not part of ES Not applicable for continuous pumping systems All Pumps on OS Operational storage component gallons Equalizing Storage ES Component For callondemand ES PHD Qs150 min but in no case less than zero ES Equalizing storage component gallons PHD Peak hourly demand gpm Maintain 30 psi QS Total of all permanent and seasonal sources gpm Required See Section 903 for sizing criteria for continuous pumping operations Low Level Alarm Fire Suppression Storage FSS Component For Single Sources and Multiple Sources FSS F190 FSS Fire suppression storage component gallons FF Needed Fire Flow rate expressed in gpm as speci ed by re authority or the Coordination Act Whichever is greater Maintain 20 psi tm Duration of FF rate expressed in minutes as speci ed by re authority or the Coordination Act Required Whichever is greater Standby Storage SB Component For Single Sources SB 733 2 days ADDD For Multiple Sources SB my 2 dayiADDD tmQsQ SB Standby storage component per local community expectations gallons T SS TMS Total for systems With a single source and multiple sources respectively ADD Average daily demand for the design year gpdERU QS The sum of the all source of supply capacities continuously available to the system gpm Q L The installed capacity of the largest source gpm N Number of ERUs t m Time that remaining sources are pumped When the largest source is not available minutes Maintain 20 psi A minimum SB volume suf cient to provide at least 200 gallons per ERU is recommended Dead Storage DS Portion of a gravity reservoir that does not provide required minimum pressure Water System Design Manual August 2001 917 FIGURE 91 RESERVOIR STORAGE COMPONENTS OVERFLOW ELEVATION PUMP A A OFF OPERATIONAL TOTAL PUMP STORAGE OS VOLUME ON I EQUALIZING EFFECTIVE STORAGE Es VOLUME ONLY A THE ES AND SB STAND BY PORTIONS APPLY TO ERU s 39 ggg DETERMINATIONS STORAGE SB AND FSS TOTAL V PUMPING A HEAD V DEAD STORAGE 20 PSIG OR 46 FEET OF HYDRAULIC HEAD BOTTOM OF FSS amp SB SECTIONS 931 amp 30 PSIG OR 69 FEET OF HYDRAULIC HEAD BOTTOM OF ES SECTIONS HIGHEST 815 amp903 I RESIDENCE I SERVED V DISTRIBUTION SYSTEM V L WHICHEVER IS GREATER SECTION 9052 ALLOWS CONSOLIDATION OF THESE COMPONENTS WITH APPROVAL OF LOCAL FIRE PROTECTION AUTHORITY WEI39 PUMP OR BOOSTER PUMP Water System Design Manual August 2001 918 Aeration Systems CE 431 0 Purpose of Aeration o In aerobic metabolism oxygen acts as the principal electron acceptor in the production of energy within a cell 0 The function of the aeration system is to transfer oxygen to the liquid at such a rate that oxygen never becomes the limiting factor in process operation 0 It is the engineers responsibility to insure oxygen is never limiting This requires an understanding of the basic principles of gas transfer as well as some familiarity with the different types of aeration devices available 0 Aeration also provides mixing 0 Fundamentals of Gas Transfer 0 General Concepts 0 The rate at which solutes diffuse across a uniform cross sectional area depends on the molecular size and shape and the concentration gradient of the substance Matter moves spontaneously from regions of high concentration toward a region of low concentration expressed mathematically as dCdy where o Cconcentration o Ydistance 0 We utilize the Stationary Liquid Film Theory 0 Simplest representation of the gas transfer process 0 Theory is based on the following concepts 0 Schematic representation Lecture Notes Aeration Systemsdoc 0 Kinetics of gas transfer 0 Mass balance for gas transfer Lecture Notes Aeration Systemsdoc 0 We then need to incorporate some correction factors 0 Temperature 0 Mixing intensity and tank geometry Lecture Notes Aeration Systemsdoc o Wastewater characteristics 0 Revised equation Lecture Notes Aeration Systemsdoc 0 Design of Aeration Systems 0 Manufacturers of aeration systems quote a figure for the oxygen transfer rate in terms of mass of oxygen that the aerator can introduce into the water per unit time per unit HP 0 Manufacturers supply the numbers under standard conditions Engineers must correct to actual conditions 0 Common types of aeration systems 0 Diffused air systems 0 Centrifugal or rotary lobe blower delivering air through a piping network to an array of diffusers installed at the bottom of the activated sludge basin 0 Most common aeration mechanism now utilized in activated sludge 0 Why 0 Submerged jet aeration 0 Typically associated with packaged treatment facilities 0 Example Sequencing Batch Reactors jet serves to mix and aerate Lecture Notes Aeration Systemsdoc 5 0 High speed surface aerator 0 Common with aerated lagoons 0 Previously utilized with activated sludge not used in this application any more 0 Why 0 Horizontal axis aerators 0 Typically utilized in oxidation ditch bioreactors to introduce air mix the wastewater and maintain a current 0 Submerged aspirating aerators Lecture Notes Aeration Systemsdoc Faculmu39ve and Aerated Lagoons CE 431 Faculmu39ve Lagoons o arge earthen basins wherein mstewater is treated through natural processes o Old technology o Simple technology to operate that is o Highly complex microbial environment o Target removal oforganic carbon settleable material and some ammonia 0 Through the use of cos y gae arge pH swings occur through the diurnal period which se as anatural disinfection method Three zones within afacultative lagoon defined by the metabolic capabilities ofthe microorganisms that thrive therein nr union 39 39 its 7 l V L m Wavy le W mnl suvtluunm 5 an m 9 H75 am luem 5 luf Wm nw mm W mom F i nemeen that s on 352mmEiisz i ii DWDacumenmEREAcademicsEE1E1LeduveNat5LedmeNat5 tantrums O 0 0000000000 Sources of oxygen Oxygen sinks NPDES permits typically 30 mgL BOD5 and 50 mgL TSS on a monthly average Why is the TSS so high relative to a typical activated sludge WWTP 30 mgL Design Typically minimum of 2 ponds o Pond 1 5075 lb BOD5acreday Oregon DEQ 50 o Pond 2 2535 lb BOD5acreday Oregon DEQ 25 o What in uences which design value you choose 0 Detention Time days Square or rectangular basins t to site Inlet amp outlet on opposite ends Inlet Outlet oriented opposite prevailing winds Clay or synthetic liners Baf ed outlet keep debrisalgae from discharge No recycle Sideslopes at 14 13 VH Dike 10 12 wide why Riprap banks why 2 4 freeboard 0 Operational Problems 0 00000 Odor nominimal water cap over anaerobic zone Organic overloading Burrowing animals Leaky liner Short circuiting Algae D My DocumenlSERC AcademCSCE 431leclure N0le5Leclure Notes 7 Lagoons doc o Biosolids Management 0 Accumulate in the pond o Dredge every 2025 years generally 0 Biosolids will often meet EPA Class B requirements Aerated Lagoons 0 Similarly configured to facultative lagoons 0 Primary difference some level of supplemental aeration o By adding 02 we increase microbiological activity which then reduces organics in the in uent wastewater Generally supplementing oxygen with mechanical aeration accomplishing complete mix would require A LOT of mechanical horsepower up to 80100 HPmillion gallons 0 Use mechanical aerators to reduceminimize short circuiting 0 Design 0 Can basically follow activated sludge approach assuming no recycle e g chemostat 0 Alternatively determine effluent BOD with a quasifirst order equation 0 k 025 to 10 d391 0 Oxygen requirement no different than activated sludge 0 Can let solids settle to bottom if not completely mixed 0 Alternately can design a clarifier after the pond D My DocumenlSERC AcademCSCE 431leclure N0le5Leclure Notes 7 Lagoons doc Preliminary Treatment CE 431 Why Preliminary Treatment Unit processes include o Influent Pump Station DMy DocumentsERC AcademicsCE 431Lecture NotesLecture Notes Preliminary Treatmentdoc 0 Screening and Shredding Screens 0 Coarse screens 6150 mm Mechanically or hand cleaned Used in small and sometimes medium sized wastewater facilities Used to protect raw water intakes Generally remove rags and larger debris Sometimes found as bypass options to more sophisticated mechanical fine screens Design considerations 0 Channel should be designed to prevent accumulation of grit etc Approach velocity 0 lt 3 fts to prevent passthrough of debris o gt 125 fts to minimize solids deposition upstream 0 Design Equation DMy DocumentsERC AcademicsCE 431Lecture NotesLecture Notes Preliminary Treatmentdoc 0 Fine screens lt 6 mm Typically mechanically cleaned Uses 0 Prelim treatment 0 Primary treatment substituting for primary clarifier o CSO treatment Configurations o Fixed 0 Rotating drum 0 Step type Design Equation 0 Microscreens lt 05pm Mechanical units continuously backwashing drumtype Filter fabric fitted over drum Wastewater flows inside drum along rotating shaft axis out through the drum Solids backwashed periodically from the drum High TSS and thus BOD removal capability Uses 0 TSS removal from secondary effluent or stabilization ponds Shredding DMy DocumentsERC AcademicsCE 431Lecture NotesLecture Notes Preliminary Treatmentdoc 0 Flow metering DMy DocumentsERC AcademicsCE 431Lecture NotesLecture Notes Preliminary Treatmentdoc o Presedimentation 0 Associated with water treatment 0 Required for raw water turbidities gt 10000 NTU 0 Either utilize smaller concrete basins for lower turbidity or large earthen ponds higher turbidity 0 May add coagulants to enhance settleability and reduce basin footprint Use of this unit process can be associated with the type of filtration employed Slow sand filtration O o Aeration 0 Most typically associated with treatment of ground water 0 Applied to remove soluble gasses C02 H28 volatile organic compounds 0 Applied to oxidize Fe and Mn to insoluble forms which can then be precipitated DMy DocumentsERC AcademicsCE 431Lecture NotesLecture Notes Preliminary Treatmentdoc 5 0 Adsorption o Utilize activated carbon Heat organic matter eg almond coconut walnut hulls wood coal to very high temp in the absence of oxygen activate by exposure to oxidizing gases such as steam and C02 at high T Yields product with highly porous structure with large surface area with slight positive and negative charges Powder or granular form 0 Will adsorb and hence remove nearly all organic compounds 0 Water Treatment odor taste and color removal Willamette River WTP uses six feet of charcoal to remove any residual turbidity pathogens organic chemicals and tasteodor compounds not already removed by prior steps in the treatment process 0 Wastewater Treatment H28 hazardous waste site remediation variety of synthetic and volatile organic compounds 0 Need to regenerate or dispose of activated carbon upon saturation Regenerating drives off the adsorbed contaminants need to keep this fact in consideration 0 Grit removal 0 Target sand silt coffee grounds and other gritty material that could cause excess weartear on mechanical equipment 0 Reactors Horizontal Flow 0 Rectangular or square 0 Grit removal predicated on water horizontal velocity less than grit downward velocity 0 Need some mechanism at the end to control the horizontal velocity at the optimum rate Need uniform distribution at the inlet Used less in lieu of more advanced technologies DMy DocumentsERC AcademicsCE 431Lecture NotesLecture Notes Preliminary Treatmentdoc 6 Aerated Grit Chambers Introduce air along one side of the tank to cause spiral flow motion along the basin axis Roll velocity controls the size of particles that will settle Need good control over the airflow rate Also washes the grit to remove organics that should remain in the process lnfluent wastewater enters in the direction of the induced roll Need to consider water volume expansion associated with aeration in determining head loss Continuously or intermittently remove accumulated grit DMy DocumentsERC AcademicsCE 431Lecture NotesLecture Notes Preliminary Treatmentdoc Vortex Grit Chambers DMy DocumentsERC AcademicsCE 431Lecture NotesLecture Notes Preliminary Treatmentdoc 0 Flow equalization DMy DocumentsERC AcademicsCE 431Lecture NotesLecture Notes Preliminary Treatmentdoc